A week and a half before Christmas, I went down to my condo’s lobby to get the mail. As expected with the holidays coming up, a slew of packages were piled up on the floor, including one immoderately duct-taped box measuring 14" x 3" x 16" with my name on it. I bent down to retrieve it with one hand: The box didn’t move. I tried next with two hands. It still didn’t move. It was then I knew that my latest TAS review assignment had arrived.
The JERN14 ES is a diminutive but hefty two-way loudspeaker with a distinctive rounded, one-piece cast-iron enclosure—“14” is the weight of the speaker in kilograms. It has limited low-frequency output and is intended for use with a subwoofer; JERN recommends the REL T/5i, a modest-sized almost-cube that the purchaser bolts to an iron damping plate (the item inside the package I found so challenging to wrangle in the lobby). There are, of course, many well-regarded speakers with cabinets made wholly or partially from aluminum. But iron? That’s a much more unusual choice. Before getting to the particulars, some background and a little metallurgy are in order.
Dansk Skalform A/S is a foundry located outside of Aars, a town on the Himmerland peninsula in northern Denmark. For more than 40 years, the firm has been producing metal parts for demanding clients, including many in the automotive realm—Porsche, Audi, and McLaren are customers. More recently, it ventured into the loudspeaker business with a subsidiary company called AudioForm. Though the design was promising, AudioForm’s cast-iron speaker was not a commercial success. Enter Ole Lund Christensen, an affable Dane with a long and wide-ranging career in audio that began during his days as an engineering student when he became the importer for KEF in Denmark. He subsequently developed several successful consumer audio brands, including Gamut, which he sold in 2004. Christensen designed one of Europe’s most sophisticated recording studios and has overseen the installation of cost-no-object music systems for wealthy audiophiles internationally. He was on the lookout for one more challenge when he encountered the AudioForm loudspeaker at a trade show. “When I knocked on the cabinet,” Christensen told me, “I immediately said, ‘This is genius!’ I told the owner of the company, Mr. [Soren] Dissing, that it was a brilliant idea. I was a bit ashamed that I didn’t come up with the idea myself because, somewhere in my memory banks, were my university books on metal technology. It’s well-known in the metal industry that if you want to reduce vibration, you use gray cast iron.” To revive the product, Dissing hired Christensen who made some significant changes that both improved the performance of the AudioForm speaker and reduced the production cost and selling price substantially. The brand was renamed JERN, Danish for “iron,” and Christensen moved from Copenhagen to Aars (population approximately 8000) to be close to the factory.
Cast iron is a family of iron/carbon alloys that have in common a low melting temperature that has obvious manufacturing utility. Disadvantages of cast iron, compared with aluminum, include low tensile strength and poor ductility—unlike aluminum, iron can’t be extruded or otherwise “worked.” Christensen’s specific mention of gray cast iron is significant: It’s the most common variety of cast iron, used to make machine-tool parts and automotive engine blocks. Slower cooling and the presence of silicon result in the formation of the graphite flakes characteristic of gray cast iron’s microstructure. In addition to lower cost, an advantage of gray cast iron over aluminum is its superior damping capacity, by a factor of several hundred. The large graphite flakes give gray CI the “constrained damping” characteristics of many more complexly engineered (and expensive) materials used for high-end loudspeaker cabinet construction.
The JERN14 ES is a distinctive-looking loudspeaker with the general form of a small sphere atop a larger one. More than one visitor saw a resemblance to the Schmoo creature from old L’il Abner comic strips (look it up). For me, the shape and heft of the JERN evokes a kettlebell at the gym—specifically, a kettlebell undergoing cell division. The enclosure is cast as a single piece and the inner surface is covered with small domes that serve to vary the thickness of the cabinet and reduce resonances (see photo). The standard finishes are a black, gray, or white “structured paint” that has a pleasantly textured feel and won’t show fingerprints or dust. There’s a high-gloss red alternative that’s very popular in JERN’s Asian market. Custom colors are available for an additional cost. JERN provides cloth covers for the two drivers that are held in place magnetically, though most users will surely leave them off for critical listening.
Two ScanSpeak drivers are utilized, a ¾" fabric dome tweeter that’s been in production for 45 years and a 5¼" glass-fiber woofer, available since 2009. Both are off-the-shelf units. The woofer performs quite well up to 9kHz, and the two drivers are crossed over at 4000Hz, an unusually high value for a two-way design. It’s the woofer’s broad functional range that allowed Christensen to implement a 6dB-per-octave crossover, instead of the fourth-order topology of the earlier AudioForm product, with just two high-quality (Mundorf) components, a coil and a single capacitor. Genuine sheep wool is placed in the center of the enclosure where it’s most helpful as a damping material, Christensen says, as air velocity is greatest away from the cabinet walls. The design positions the tweeter behind the plane of the woofer, assuring correct time alignment of the two drivers. Internal wiring is with vibration-resistant, Teflon-insulated, silver-coated copper cable. The rear of the enclosure sports a single pair of WBT 0703cu Nextgen binding posts.
As the JERN14 ES is a sealed-box design, bass falls off at a rate of 12dB per octave below 100Hz; for any real-world scenario, low frequency augmentation is going to be needed. JERN, as yet, doesn’t make a subwoofer and suggests the REL, a compact (10.5" x 12.5" x 12.7"), non-ported design with a single down-firing 8" driver. This sub provides a –6dB in-room response down to 32Hz, which doesn’t represent pant-leg-flapping bass in the lowest octave but is appropriately scaled to the dynamic capabilities of the 14 ES. The T/5i has a 125-watt Class AB amplifier onboard that will accept a line-level signal from a preamplifier, but REL and JERN—and yours truly—strongly recommend using the high-level input, which takes signal from the same amplifier(s) powering the main speakers. REL supplies a 10-meter interconnect with bare wires at one end to connect to the positive terminals of the right and left channels of your power amplifier(s) and a Neutrik speakON plug that connects to the subwoofer. With this option, the amplification for the sub, obviously, is identical in character to that provided to the JERNs, and the integration of sub and satellites is very effective. In comparison, running the REL as an active subwoofer via a long RCA-to-RCA cable from a preamp’s “.1” output resulted in the all-too-familiar sound of limited LF main speakers paired with a boomy sub. Actually, Christensen doesn’t want us to think of the JERN/REL combination as a satellite/subwoofer system but, rather, as a three-way loudspeaker in which the bass driver, shared by both channels, happens to be in another cabinet.